1. Field of the Invention
The present invention relates to a sensor equipped wheel support bearing assembly having a load sensor built therein for detecting a load imposed on a bearing unit rotatably supporting a vehicle wheel.
2. Description of the Prior Art
For safety travel of an automotive vehicle, the wheel support bearing assembly equipped with a sensor for detecting the rotational speed of each of vehicle wheels has hitherto been well known in the art. While the automobile traveling safety precaution is generally taken by detecting the rotational speed of the respective vehicle wheel in various locations, it is not sufficient with only the rotational speed of the vehicle wheel and, therefore, it is desired to achieve a control for safety purpose with the use of other sensor signals.
In view of the above, it may be contemplated to achieve the vehicle attitude control based on a load acting on each of the wheels during travel of an automotive vehicle. By way of example, a large load acts on the outside wheels during the cornering, on the wheels on one side during the run along left and right inclined road surfaces or on the front wheels during the braking, and, thus, an equal load does not act on each of the vehicle wheels. Also, even in the case of the uneven live load, the loads acting on those wheels tend to become uneven. For this reason, if the loads acting on the wheels can be detected as needed, suspension systems for the vehicle wheels can be controlled beforehand based on results of detection of the loads so that the attitude control of the automotive vehicle during the traveling thereof (for example, prevention of a rolling motion during the cornering, prevention of diving of the front wheels during the braking, and prevention of diving of the vehicle wheels brought about by an uneven distribution of live loads) can be accomplished. However, no space for installation of the load sensor for detecting the load acting on the respective vehicle wheel is available and, therefore, the attitude control through the detection of the load can hardly be realized.
Also, in the event in the near future the steer-by-wire is introduced and the system, in which the wheel axle and the steering come not to be coupled mechanically with each other, is increasingly used, information on the road surface comes to be required to transmit to the steering wheel by detecting a wheel axis direction load.
In order to meet those needs hitherto recognized, the Japanese Published International Application No. 2003-530565 suggests a wheel support bearing assembly, in which a strain gauge is affixed to an outer ring of the wheel support bearing assembly for the purpose of detecting strains.
An outer ring of the wheel support bearing assembly is a bearing component part having a rolling surface defined therein and required to have a strength, which bearing component part is manufactured through complicated process steps including, for example, a plastic forming, a turning process, a heat treatment and a grinding process. Accordingly, where a strain gauge is attached to the outer ring such as disclosed in the prior art document referred to above, there is a problem in that the productivity is low and the cost of manufacture thereof during a mass production tends to become high. Also, it is not easy to detect a strain occurring in the outer ring with high sensitivity and, when a result of such detection is utilized in controlling the vehicle attitude of an automotive vehicle then traveling, a problem will arise in association with the accuracy of the control.
In view of the foregoing, attempts have been made to secure a strain sensor to a sensor mounting member to form a sensor unit, which is in turn fitted to a peripheral surface of the outer member. In such case, when a sensor signal processing circuit for processing an output from the strain sensor is provided in the wheel support bearing assembly, the wiring from the strain sensor to the sensor signal processing circuit can be simplified as compared with the case in which the sensor signal processing circuit is provided in an electric control unit (ECU) of an automotive vehicle. However, since no extra space is available in the wheel support bearing assembly and, therefore, the position for installation is limited, a problem is encountered with as to how and where the sensor signal processing circuit is installed in the wheel support bearing assembly. In addition, it is a prime concern and is keenly desired to provide the sensor signal processing circuit with high productivity and inexpensively and also to avoid reduction in assemblability of the sensor unit.